Difficult theoretical problem on basis vectors

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Discussion Overview

The discussion revolves around proving the uniqueness of vector components with respect to a given basis. It explores theoretical approaches to understanding this concept, including the implications of vector independence and the structure of proofs in linear algebra.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant expresses confusion about how to start proving the uniqueness of vector components.
  • Another participant proposes a hypothetical scenario where vector components are not unique and outlines a mathematical approach to show that this leads to a contradiction based on the independence of basis vectors.
  • A third participant acknowledges the logic of the previous point but emphasizes the difficulty in approaching the problem initially.
  • A later reply suggests a general strategy for proving uniqueness by presenting two elements and demonstrating their equality, referencing a specific proof as a guide.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the easiest way to approach the proof, indicating that the discussion remains unresolved regarding the best starting point and methodology.

Contextual Notes

Some assumptions about the definitions of basis and vector independence are present but not explicitly stated. The discussion reflects varying levels of comfort with the proof process.

spaghetti3451
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How the hell do you prove that the components of a vector w.r.t. a given basis are unique?

I have literally no idea how to begin! It's just that with these theoretical problems there's no straightforward starting point!
 
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Suppose they were not unique. That is, suppose there were some vector, v, such that
[tex]v= a_1v_1+ a_2v_2+ \cdot\cdot\cdot+ a_nv_n[/tex]
and
[tex]v= b_1v_1+ b_2v_2+ \cdot\cdot\cdot+ b_nv_n[/tex]
Now subtract:
[tex](a_1- b_1)v_1+ (a_2- b_2)v_2+ \cdot\cdot\cdot+ (a_n- b_n)v_n= 0[/tex]

One of the requirements for a "basis" is that the vectors are independent. Use the definition of "independent".
 
I see! If the basis vectors are independent, then the coefficients are zero, that is, the components are unique.

I have to tell you, though! It's not easy to figure out how to go about the problem.

I just wish the solution were as obvious as it looks now!
 
If it helps, the general pattern of any proof about "uniqueness" is to present two elements, and deduce that they are the same. The first two lines of Halls' proof are exactly that... and starting is usually the hardest thing. Once into it, you'll figure out a way of proving that your two elements are equal.
 

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